A general programmable logic controller contains a microprocessor and is connected to electronic loads such as various kinds of actuators and display devices. The programmable logic controller drives and controls the electronic loads according to a sequence program stored in a memory and operation states of the electronic loads represented by input signals that are sent from operation switches, various kinds of sensors, etc.
A programmable logic controller of a related art is used together with a special unit which mounts an integrated circuit element and an input/output interface circuit each for performing high-speed input/output processing. The special unit operates as an input/output control device. The integrated circuit element mounted on the special unit includes a parameter memory and a logic circuit part. Operation specification of each of the parameter memory and the logic circuit part is determined according to content of a special instruction within a program memory. A reversible counter constituting the logic circuit part is used for both the high-speed input processing and the high-speed output processing (see Patent Document 1, for example).